The present invention relates to a lithium-ion secondary battery wherein anodes and cathodes are separated and bound by two different porous layers of polymeric materials containing particulate matter, and methods for fabricating the same.
Lithium-ion polymer batteries are fabricated by various methods. In U.S. Pat. No. 5,536,278 an electrolyte film, previously prepared, is heated and laminated to a first electrode. The second electrode is then laminated to the laminated first electrode.
In U.S. Pat. No. 5,778,515 an electrode film and a separator film are formed then laminated after use of a pre-lamination solvent on the surface at least one of the films.
In U.S. Pat. No. 6,024,773 a separator film is coated on both sides with a binder resin solution so as to bond the electrodes with the separator film separating them.
In U.S. Pat. No. 5,348,824 polymer based amorphous compositions are melt extruded in the form of a thin film directly on the positive electrode of a lithium battery.
In all of the processes in which a sheet or film is formed, the composition of the separator material is limited to polymers having satisfactory mechanical strength for forming a thin film and for carrying out the laminating process with the electrodes. Use of particulate material in the polymer, to any great extent, is nearly impossible with any polymer as the mechanical strength is decreased further with the addition of the particulate material. In melt extended polymers, the porosity is difficult to control and is typically low.
Those disadvantages and other are overcome with use of the present invention.
The present invention is concerned with a Li-ion polymer battery and methods for its fabrication. Two layers of differing polymeric materials are provided, in non-sheet form, to separate and bind adjacent anodes and cathodes (electrodes) of the battery. The Layers contain a particulate material to increase porosity of the layers. The differing polymeric materials have specific solubility requirements which are described below.
The battery has at least one anode and at least one cathode which is in opposing spaced relationship to each anode. Two layers of differing porous separators/binders are intermediate each anode and cathode to maintain the spacing and to bind each anode to each cathode. A non-aqueous electrolyte fills the pores of the separators/binders. Each separator/binder consists of a polymer and particulate material. A first separator/binder is made up of polymer P1 and particulate material M1; the second separator/binder is made up of polymer P2 and particulate material M2. The polymers and particulate materials must have solubility properties such that P1 is soluble in solvent S1, P2 is soluble in solvent S2, P1 is non-soluble in solvent S2, P2 is non-soluble in solvent S1, M1 is non-soluble in S1, and M2 is non-soluble in S2.
Preferred structures of the batteries are a prismatic form (stacked) and a cylindrical form (wound). Fabrication is carried out by three fabricating methods. In all of the methods the first separator/binder, in which the polymer is dissolved in a solvent, is applied to the electrodes in such a manner that a single layer of the first separator/binder will be present between each anode and cathode in the completed battery. The first separator/binder is then dried. The second separator/binder is provided in differing manners in each of the three methods, however the polymer of the second separator/binder is in at least a partially dissolved condition while the electrodes are in a stacked form in order that the electrodes are bound in either the prismatic or cylindrical form when the second separator/binder is dried by evaporation of the solvent S2.
In a first method the electrodes are stacked while the second separator/binder is not fully dried and in a tacky condition.
In a second method the electrodes are stacked with only the first separator/binder between them and the second separator/binder is infiltrated to between the electrodes and then dried.
In a third method the electrodes are stacked with a first and a second separator/binder, in a dried condition, between them; solvent S2 is then infiltrated to between the electrodes so as to at least partially dissolve polymer P2 such that when dried the electrodes will be bound together.
Final fabrication of the batteries, in all three methods, includes providing a non-aqueous electrolyte to fill the pores of the separators/binders and packaging the electrodes and electrolyte.